The present invention mainly relates to a semiconductor light emitting device that includes a nitride group semiconductors (e.g., general formula InxAlyGa1-x-yN (0≦x, 0≦y, x+y≦1), and a method for producing this semiconductor light emitting device.
Semiconductor light emitting devices that include a light emitting layer between p-type and n-type semiconductor layers have been practically used as light emitting diodes (LED), semiconductor laser diodes (LD), and for lightings that employ the LEDs or LDs, and the like. In particular, since semiconductor light emitting devices that include nitride group materials (hereinafter, occasionally and generically referred to as “GaN”) can emit blue or green light, these semiconductor light emitting devices have been energetically researched and developed.
As a method of producing these semiconductor light emitting devices, it is known that GaN is grown on a different material substrate. In this method, after the different material substrate is subjected to a thermal cleaning treatment, a low-temperature buffer layer is grown on the upper surface of the different material substrate. Subsequently, a GaN layer is grown at a high temperature. The purpose of GaN layer growth is to make the substrate surface flat, and to eliminate penetrating pits from the different material substrate. Subsequently, an n-type contact layer is grown which is an n-type-impurity-doped layer and provide an ohmic contact surface onto which an n-side ohmic electrode is formed. Subsequently, a superlattice layer is deposited as a primary layer for an active layer. After that, the active layer is grown.
In this production method, since GaN is grown on the different material substrate, a number of dislocations will extend from the GaN layer through the n-type contact layer and the active layer to the p-type semiconductor layer. In particular, in the case where the active layer includes In, crystal defects present. The crystal defects have relationship with the amount of dislocations from the primary layer. That is, the crystal defects will increase with dislocations. as a result, non-light emission recombination probability will greatly depend on the dislocations.
On the other hand, in order to provide a high intensity and efficient light emitting device, the thickness of a well layer and the number of layers in the active layer are increased (for example, Patent Literatures 1 to 5). For example, according to Patent Literature 1, in an active layer having a semiconductor quantum well structure that includes barrier and well layers, the well layers have different thicknesses whereby emitting light with different wavelengths. In addition, the number of pairs of the barrier and well layers is greater on the p-side semiconductor layer side than the n-side semiconductor layer side. Also, according to Patent Literature 2, the p-type impurity doping amount is small or the p-type impurity is not doped in a p-type semiconductor layer close to the active layer, while a barrier layer that is the closest to the p-type semiconductor layer side is formed thin so that the hole injection efficiency can be improved.